1. Field of the Invention
The present invention relates to plunger type solenoids and more particularly to solenoids having plungers the speed of movement of which is easily controlled.
2. Description of the Prior Art
Plunger type solenoids are widely employed for various uses, for instance, as an automatic control device, a remote handling system, an automatic numerical control (NC) device or a data processing apparatus. A feature of the plunger type solemoids is that they may be operated with a high degree of reliability. However, the speed of the plungers is practically difficult to control because the mechanical output thereof is small compared to their high speed. In drive systems for various control devices, the speed of operation must be controlled. Accordingly, the plunger type solemoids must be provided with speed controllers when used in control devices.
In plunger type solemoids, an efficient speed control is very difficult to achieve if an energy loss occurs, because the mechanical output of the solenoid is small, as set forth above. Therefore, friction resistance must be reduced to an extreme extent to provide satisfactory speed control.
Further, the inventor has discovered that the speed of the plunger increases suddenly as the stroke of the plunger approaches the zero or end position. In general, the speed of the plunger is proportional to the attractive force of the coil thereon, so that the chracteristic speed build-up of the plunger must be linear, to avoid wear and to lengthen the life of the apparatus to which the solenoid is attached.
Accordingly, it is an object of the present invention to provide plunger type solenoids having plungers the speed of which are easily controlled with high reliability.
It is another object of the present invention to provide plunger type solenoids in which friction resistance is eliminated during operation, to thereby provide an excellent durability.
It is a further object of the present invention to provide plunger type solenoids which are provided with an adjusting device to provide a fine speed control.
It is a still further object of the present invention to provide plunger type solenoids, the speed characteristic of which is linear.